With increased demand for mobile communication throughput, it is required that in an area covered by a Marco cell, operators deploy a Pico cell aiming at implementing high throughput according to specific throughput requirements. In order to avoid to intra-frequency interference between cells, the operators may choose to deploy the macro cell and the pico cell on different carriers. In the hierarchical HetNet with the inter-frequency deployment of the macro cell and pico cell, the conventional measurement aiming at seamless switching brings a lot of unnecessary inter-frequency measurements to the UE. In order to improve the conventional inter-frequency measurement aiming at instant switching, the 3GPP sets up a special research project for researching a measurement strategy aiming at load balancing in a hierarchical HetNet of the inter-frequency deployment.
In the moving process of the User Equipment (UE), in order to maintain the continuity of the service, the UE needs to continuously detect and measure the current serving cell and neighboring intra-frequency/inter-frequency cell. The measurement performed by the UE includes: Reference Signal Receiving Power (RSRP) and Reference Signal Receiving Quality (RSRQ).
RSRP represents receiving power of a reference signal and is for measuring the power of a Resource Element (RE) of a cell reference signal.
The RSRQ represents the receiving quality of the cell reference signal. The value of the RSRQ is equal to N*RSRP/(RSSI). N is a number of resource blocks. RSSI is a strength indicator of a received signal and includes power of a serving cell, a non-serving cell and a thermal noise.
In order to measure the inter-frequency cell, the UE needs to adjust working frequency of a receiver according to an inter-frequency frequency point. In order to guarantee that the service of the current serving cell is not interrupted, the serving cell will configure a measurement gap with a period of 40 ms or 80 ms and with a length of 6 ms for inter-frequency measurement. The UE identify and measure the inter-frequency cell in the configured measurement gap. As for the measurement aiming at the mobile switching, in order to guarantee the balance between the frequency points, the UE measures the inter-frequency frequency points configured by the eNBs adopting a mechanism of sequential measurement.
The measurement of the inter-frequency cell performed by the UE includes two steps, i.e. cell identification and cell measurement. As for a new cell, the UE performs synchronization of carrier frequency adopting information of the frequency point notified by the current serving cell, performs timing synchronization adopting primary synchronization and secondary synchronization signals, and determines a physical layer identifier of a cell. As for an identified cell, i.e. the cell, on which time and frequency synchronization is performed and the physical layer identifier of which is determined, the receiving power and receiving quality is measured according to the reference symbol, and the report is made according to a measurement event configured by the eNB.
A current LTE network eNB may configure the UE for measuring the serving cell and the neighboring cell and reporting a measurement message, to control the mobility of the UE. In order to limit the number of signalings sent to the eNB, a measurement and reporting event may trigger the measurement and reporting through the eNB configuration. The LTE single carrier system defines following event triggering and reporting standards:
Event A1: measurement result of the serving cell is better than an absolute threshold;
Event A2: the measurement result of the serving cell is worse than the absolute threshold;
Event A3: the measurement resulting of the neighboring cell is better than an offset of the serving cell; and
Event A4: the measurement result of the neighboring cell is better than the absolute threshold.
When one or multiple cells satisfy a designated entering condition, the UE triggers an event. The eNB may set configurable parameters used in these conditions to affect the entering condition. In order to trigger the event, the entering condition at least satisfies the conditions in the time to trigger configured by the network.
The current LTE network eNB may configure the UE according to the service condition of the UE to let the UE perform a Discontinuous Reception (DRX) scheme, so that the UE may discontinuously monitor a Physical Downlink Control Channel (PDCCH) the serving cell. At the same time, the UE may choose not to measure the serving cell or the neighboring cell in a configured sleeping stage of the configured DRX, while the associated measurements in a DRX On-Duration is performed, to save the UE measurement power consumption.
As for a performance index of the cell identification and cell measurement, a related 3GPP standard respectively defines the minimum requirements of the maximum time requirements of the cell identification and cell measurement. That is, the UE needs to finish the measurement and reporting of the cells satisfying the above conditions within the maximum time requirement. The minimum requirement is defined in the related 3GPP standard according to cell identification ability of the UE. The time requirement is a fixed time length if the DRX is not configured. If the DRX is configured, the time requirement is an integer multiple of a DRX cycle.
In a hierarchical HetNet of the inter-frequency deployment, the target for deploying the carrier of the pico cell is to balance the load of the macro cell, to enhance the throughput of the system. The measurement of the carrier aiming at the load balance has characteristics related to the UE service. That is, as for the UE with relatively low requirements on the throughput, the operation of quickly and timely switching the UE to the pico cell not only cannot improve the whole performance of the system, but also increases the UE measurement power consumption. In addition, as for an area, in which the pico cells are deployed with a low density, if a UE with a low moving speed frequently identifies the cells on the pico cell carrier, the UE measurement power consumption is inevitably enhanced. At the same time, from the point of view of the system performance, the existing measurement accuracy and switching performance cannot be enhanced. Therefore, the identification and measurement of the cell on the specific carrier needs to be improved, to guarantee the balance between the UE measurement power consumption and the system performance.